1. Field of the Invention
This invention relates in general to a toner for forming an image, a developing method and a developing device. More specifically, the invention relates to an image formation toner that contains metal materials serving as the fixing aids and the coloring agent, a developing method and a developing device.
2. Description of Related Art
In general, as disclosed in U.S. Pat. No. 2,297,691, Japanese Laid Open S49-23910 and Japanese Laid Open S43-24748, the image formation of the electrophotography utilizes various methods to form an electric latent image on a photosensitive body that is made from a photo conductive material. After the electric latent image is developed by a developer, the image formed by the developer is transcribed onto a medium, such as a paper according to the requirement, and then the transcribed image is fixed by heating, pressing or solvent vaporizing.
The methods for developing the electric latent image can be roughly classified as follows. One is the liquid developing method and the other is the dry developing method. The liquid developing method uses a liquid developer that various colors and dyes are dispersed in an insulating organic liquid. The dry developing method uses a dry developer (a toner, hereinafter) that the coloring agent, such as the carbon black, is dispersed in a natural or a synthetic resin by the cascade method, the magnetic brush method, the powder cloud method etc. The dry developing method is widely used recently.
In general, a heat roller is widely used as a fixing method (fixation) for the dry development in consideration of the excellent energy efficiency. Lately, in order to save energy by the low temperature fixation of the toner, the heat energy provided to the toner during the fixation tends to become smaller. In 1999, the International Energy Association (IEA) published a specification required by a Demand-Side Management (DSM) program for the technology project of the next generation copy machine. In the specification, for a copy machine higher than 30 cpm, power consumption is lower than 10˜30 Watts (dependent on the copy speed) within a standby time of 10 seconds. The energy is considerably saved in comparison with the conventional copy machine.
For the low temperature fixation property, a polyester resin that is superior in the low temperature fixation property and the thermal preservation resistance property has been tried to use to replace the conventional styrene-acryl resin (referring to Japan Laid Open S60-90344, S64-15755, H2-82267, H3-229264, H3-41470 and H11-305486 etc). However, even though the conventional well-known technology is suitable, it is impossible to achieve the specification of the DSM program. Research and study into the low temperature fixation is necessary for improving the conventional technology.
For low temperature fixation, the thermal properties of the resin have to be well controlled. However, when the glass transition temperature is reduced too much, the thermal preservation resistance property becomes worse. When the molecular weight is reduced and the softening temperature of the resin is lowered too much, the temperature where the hot offset occurs is reduced. Therefore, it is impossible to obtain a toner having an excellent low temperature property and a higher temperature for the hot offset.
For preventing the hot offset, it is well known that a releasing agent, such as the wax, can be included in the toner, and the wax is exuded from the toner during fixation (referring to Japan Laid Open H7-295290, H8-234480, H9-034163, H2000-56511, and Japan Patent No.2904520, etc). The releasing agent has to be dominant in the toner because it is easily exuded. However, the wax (releasing agent) on the surface of the toner particles becomes too great because of the dominance of the releasing agent, which causes problems with the preservation and the development properties. In particular, for a fixing system where the fixing unit (such as a heat roller) has a low heat capacity and the temperature response of the toner is increased, the surface pressure of the roller must be reduced for thinning the heat roller. Therefore, the releasing agent is hard to be exuded, and exuding is difficult because the releasing agent is dominant in the toner.